Backhoes, excavators and similar types of vehicles have an articulated arm assembly with a boom arm pivotally connected to the vehicle and a dipper stick pivotally attached to the boom arm at an end remote from the vehicle. The arm assembly usually has a bucket pivotally attached at the free end of the dipper stick. Generally, the articulated arm assembly is pivotally connected to the vehicle so that the arm assembly can be rotated about a vertical axis relative to the vehicle, or is attached to a cab with the cab and arm assembly being rotatable as a unit about a vertical axis relative to the vehicle undercarriage. The bucket is pivotally attached to the dipper stick by a clevis which serves as a pivot point for the bucket relative to the dipper stick. The bucket is rotatable about the dipper stick pivot point in a generally vertical plane containing the boom arm and the dipper stick. While the entire articulated arm assembly can be rotated relative to the vehicle, the dipper stick and attached bucket could not be rotated about the longitudinal axis of the dipper stick. Thus, the dipper stick and attached bucket could not be rotated independent of the boom arm.
There are occasions, however, when it would be very desirable to be able to rotate the dipper stick and hence the bucket independent of the boom arm so that the bucket can work along a cut line out of the plane containing the boom arm and the dipper stick. This would allow an operator to dig an offset ditch, such as a ditch running along a straight cut line at a distance to the side of the vehicle, without moving the vehicle. Of course, when digging such a ditch it is desirable to keep the bucket in alignment with the cut line at all times to provide a ditch having the precise width of the bucket being used. Without being able to rotate the dipper stick about its longitudinal axis, in the past, this meant aligning the vehicle so that the plane containing the boom arm and the dipper stick was in coincidence with the cut line. It was not possible to park the vehicle off to the side of the ditch and spaced away from the cut line, such as is sometimes desirable, and dig a narrow ditch along the cut line.
Being able to rotate the dipper stick also would allow the operator much greater flexibility in the cut being made by the bucket in other situations and minimize the number of vehicle moves necessary to accomplish the cut desired. One example is the digging of a box hole with a square corner where the bucket must dig from two directions at right angles to each other to make a clean corner cut. Another example is digging around piles and other obstacles, or digging several ditches at different angles, such as a main and branch water supply or drainage ditches. It is very desirable to be able to complete such cuts without moving the vehicle. Being able to rotate the dipper stick enables the operator to perform such digging jobs with little or no movement of the vehicle, and also to lift or manipulate objects, such as rocks or slabs from all angles without moving the vehicle. The ability to rotate the dipper stick allows the operator to conveniently perform additional jobs, such as rotating the dipper stick in one direction to pick up material, and then rotating the dipper stick by 180.degree. or as desired and extend the articulated arm to deliver the material to another place.
The increased versatility noted above has been realized with the advent of the rotatable dipper stick. In the past, such rotatable dipper stick units have utilized a dipper stick with a boom attachment head comprising a large turntable bearing with a ring gear machined into the perimeter of the rotatable turntable bearing member. A hydraulic motor with a pinion gear in engagement with the turntable gear provided the rotational drive. A brake was used to stop the rotational movement when desired and to hold the rotational position of the turntable bearing member while the dipper stick was being used to dig. This arrangement is bulky, heavy and lacks precision control both during rotation of the dipper stick and when being held in position while work is being performed. The resulting dipper stick assembly is much larger than a conventional non-rotatable dipper stick and larger than desirable for all but the largest excavation vehicles. Further, such a design arrangement cannot be reduced in size for use in the smaller sized dipper sticks necessary for smaller-sized backhoes and excavators. While such rotatable dipper sticks have existed for several years, the drive mechanisms used have not provided optimum results.
It will therefore be appreciated that there has been a significant need for a rotatable dipper stick rotated by a mechanism able to transmit a large torque to the dipper stick and firmly hold the dipper stick in the desired rotational position even under large work loads. Preferably, the rotatable dipper stick should be rotatable through more than 360.degree.. The rotatable dipper stick should be smaller and lighter than those presently available, and fit within the normal dimensional envelope of presently existing conventional nonrotatable dipper sticks. The rotatable dipper stick should also be effectively and economically manufacturable in small as well as large sizes. Moreover, the rotatable dipper stick should have a precision rotational drive mechanism capable of precise positional control and able to hold its rotational position without the use of a separate brake mechanism which can slip or fail. The rotatable dipper stick should also be able to operate without failure when subjected to large side loads. The present invention fulfills these needs and further provides other related advantages.